The ability to reproduce music by operating musical instruments by mechanical means can be traced back at least to the sixteenth century. All such systems require some form of memory and this has in the past taken many forms, notably pins set in cylinders or discs, or holes punched in paper or card. More recently the required information has been stored magnetically on tape or disc, and it is now possible to store such information in solid-state memories requiring no mechanical movement to record (write) and playback (read). The present invention is concerned primarily with the use of solid-state memory, although it may be, and usually would be, associated with magnetic recording used as back-up.
It is necessary to draw a distinction between digital recording of information characterising the actions of the musician in playing an instrument and the recording of a digitised version of an analog electrical signal derived from the sound of the instrument by means of a microphone or, in the case of certain modern instruments, derived from the signal fed to a loudspeaker. The latter method requires the use of a very large number of bits of memory and is, at present, not practicable in solid-state except possibly for very short bursts of sound. The present invention is concerned only with the digital recording of information characterising the actions of the musician. The present invention assumes that the musical instrument to be recorded and played back is, or can be made, able to furnish signals in electrical form characterising the operation of the instrument and is, or can be made, able to playback when supplied with such signals generated electrically. This means that the invention is, for practical purposes, restricted to keyboard instruments such as the organ, piano and harpsichord which can be fitted with electrical contacts on all the controls, but includes such instruments as the xylophone and vibraphone which, although not normally played from a keyboard, can be so adapted, as has been done in the past in organs used for playing popular styles of music.
It will be shown that where proper reproduction of the instrument requires the storage of signals characterising the force with which notes are struck, the present invention is capable of storing such signals and possibly of assisting in their generation but no claim is made for teaching any basic method of deriving such signals.
It is desirable to draw a distinction between two basically different methods for generating the signals needed for the recording process. Recording in "real time" requires the music to be actually performed by a musician having the necessary degree of manipulative skill; but it is also possible with a suitable recording medium to key-in, without reference to lapse of real time, the necessary data without recourse to the services of a manually-skilled musician. The latter process is very time-consuming and tedious and usually results in an impersonal playback which is unacceptable to serious musicians. The present invention is mainly directed to real-time recording of "live" performances, but it also affords the possibility of editing, by computer techniques, or even complete off-line recording, thus achieving the best of a combination of both methods. This is of value, for example, in changing the recorded registration (stop settings) of an organ without the need for the original performance to be repeated.
The cost of solid-state digital storage is at present in the order of a tenth of a cent (US) per bit. The number and range of notes and other controls used in a substantial piece of music is such that a high degree of economy in the use of such storage is necessary if the system is to be economic and practicable. This matter will be discussed in detail with reference to a fairly small pipe organ. It is to be understood that the arguments can readily be extended to large instruments.